This invention relates generally to a means for the filtration of a particulate-laden fluid, and more particularly, to a means for filtering such a fluid and returning the filtered particulates to an associated reactor vessel without external handling.
Raw product gases leaving a reactor vessel such as a coal gasifier often contain many impurities which must be removed prior to the gas end use. In particular, product gas leaving a coal gasifier typically contains entrained coal fines and condensible constituents such as vaporized tar which must be removed prior to an end use for the gas such as in a gas turbine in an integrated coal fired plant. Various systems have been proposed for the removal of the entrained coal fines including a gas quench system such as that included in the coal gasification power plant described in U.S. Pat. No. 4,150,953 (Woodmansee). Another proposed approach is the use of a high temperature cyclone such as described in copending U.S. pat. application Ser. No. 919,460 (Giles) filed June 27, 1978 now U.S. Pat. No. 4,212,653 and assigned to the assignee hereof. Once they are removed, the coal fines are preferably recycled back to the gasifier for a more efficient utilization of coal resources.
In a quench system hot raw gas is cooled by direct contact with a water spray. A certain portion of the tar vapor is condensed by this cooling process, and this condensed with some water and most of the coal fines is removed from the gas in the form of a suspension herein referred to as "sludge". The removal of this sludge from a quench vessel is complicated by the fact that the sludge is viscous and thus adheres to and fouls valves, pumps, and pipes with which it comes into contact. This problem is aggravated during a plant startup from a cold condition since any solidified sludge in an associated cleanup system must first be liquified by the addition of heat before the plant is fully operable. Moreover, since the coal fines are relatively small and light some of the fines may remain suspended in the water which is conventionally recycled back to the quench through a recirculation system where these suspended fines may cause additional plugging.
In contrast to gas quench systems, cyclone separators are capable of operating at temperatures in excess of the tar condensation temperature and thereby avoid the problems associated with handling viscous tars. Additionally, cyclone separation enables a separate removal of particulates and a later removal of tars which may be advantageous in the maintenance of prescribed tar and coal fines feed ratios into a recycling system such as the extruder disclosed in U.S. Pat. Nos. 4,049,390 and 4,049,392 (Furman).
However, cyclone separators have encountered operating problems including erosion and plugging of the outlet cone. For example, cyclone separators during a startup from a cold condition initially operate at a temperature below the tar condensation temperature, potentially resulting in plugging and fouling of the cyclone by condensed tar. Furthermore, the beneficial recycling of coal fines to achieve a more efficient coal utilization still requires additional external handling whether they are recycled from a cyclone separator or from a gas quench system. This external handling necessarily results in increases in both manpower and equipment as well as in the increased potential for detrimental fouling, plugging and erosion.
Accordingly, it is an object of the present invention to provide a new improved means for the filtration of particulates from a raw fluid stream.
Another object of the present invention is to provide a means for filtering particulates from raw coal gas in the absence of condensed tar.
Still another object of the present invention is to enable the recycling of particulates to the reactor vessel without external handling.